Radio communication system, radio communication method, and radio communication device

ABSTRACT

In the environment of a communication area including a SDM-compatible mobile station for space division multiplex transmission and a SDM-uncompatible mobile station not compatible with space division multiplex transmission, a base station having a plurality of antennas and capable of adaptively changing directivity performs allocation of a mobile station which simultaneously performs space division multiplex transmission (SDM) and space division multiplex access (SDMA) by using a predetermined space division multiplex transmission evaluation criterion and a space division multi access evaluation criterion. By using this radio communication method, it is possible to use the spatial degree of freedom at its maximum and provide a radio communication system having an improved communication capacity.

This application is a U.S. National Phase Application of PCTInternational Application PCT/JP2003/015605.

TECHNICAL FIELD

The present invention relates to a radio communication system usingspace division multiple access and space division multiplex, and moreparticularly to a radio communication system, radio communication methodand apparatus for same, adapted to determine the applicability of andapply both simultaneously or any one of space division multiple accessand space division multiplex transmission in accordance with propagationenvironment, traffic status and the like where there are coexistingmobile stations compatible with space division multiplex transmissionand mobile stations uncompatible therewith, within a communication area.

BACKGROUND ART

Recently, there is an increasing demand toward the increase in thecapacity and speed of radio communication. Studies are vigorous as tothe methods for improving the effective utilization ratio of definitefrequency resources, as one method of which attentions are drawn to thetechnique to make use of space domains. The space-domain utilizationtechniques includes, as one, an adaptive array antenna (adaptiveantenna) wherein, by adjusting the amplitude and phase by means of aweighting coefficient for multiplication on a received signal(hereinafter, referred to as “weight”), reception is intense for thesignals arriving in a desired direction, thus enabling suppression indirections of interference waves. This can improve the communicationcapacity for the system.

Meanwhile, there are other arts utilizing space domains, i.e. 1) spacedivision multiple access technique for transmission to different mobilestations (hereinafter, referred to as “SDMA” wherein SDMA is anabbreviation of space division multiple access) and 2) space divisionmultiplex technique for transmission to the same mobile station(hereinafter, referred to as “SDM” wherein SDM is an abbreviation ofspace division multiplex), of different data sequences by use of thephysical channels same in time, frequency and sign through utilizationof a spatial orthogonality over the propagation path. The SDMA techniqueis disclosed of information in JP-A-2002-261670 and in Document T.Ohgane et al, “A study on a channel allocation scheme with an adaptivearray in SDMA,” (IEEE 47th VTC, Page(s): 725-729 vol. 2 1997). Where thespatial correlation coefficient between mobile stations is lower than apredetermined value, SDMA is available thus making it possible toimprove the throughput of a radio communication system and the number ofsimultaneous active users.

Meanwhile, the SDM technique is disclosed of information inJP-T-2001-505723 and in Document G. J. Foschini, “Layered space-timearchitecture for wireless communication in a fading environment whenusing multi-element antennas,” (Bell Labs Tech. J, pp. 41-59, Autumn1996), wherein the transmitter and the receiver both has a plurality ofantenna elements thus realizing SDM transmission under the propagationenvironment low in received signal correlation between the antennas. Inthis case, different data sequences are sent from a plurality ofantennas provided on the transmitter by use of physical channels same intime, frequency and sign on an antenna-element-by-antenna-element basis.At the receiver, demultiplex-reception is made based on different datasequence from the received signal at a plurality of antennas provided onthe receiver. This allows to achieve speed increase by use of aplurality of space division multiplex channels instead of usingmulti-level modulation. In implementing SDM transmission, communicationcapacity can be increased in proportion to the number of antennas oncondition that the transmitter and the receiver have the equal number ofantennas, in an environment that a multiplicity of scatterers existbetween the transmitter and the receiver under satisfactory S/N(signal-to-noise ratio) conditions.

However, in the conventional SDM art, the maximum number of spacedivision multiplex ones undergoes restriction at the end of transmitterand receiver which is less in the number of antennas. Consequently,where there is a deviation in the number of transmission and receiveantennas, space division multiplex is possibly not utilized efficientlyunder certain propagation environments. Particularly, because antennaelements can be set up greater in the number at the base station endthan at the mobile station, there arises a case to cause a room for thedegree of spatial freedom in transmission of from the base station tothe mobile station. Meanwhile, in order to make the mobile stationcompatible with SDM, there is a need for a plurality of antennas, aplurality of transmission or reception systems and a signal processingsection for demultiplexing a space-division-multiplexed signal, thusraising cost. For this reason, it can be considered that the mobilestations not compatible with SDM coexist within the communication area,thus requiring a method for space division multiple access undercoexistence of mobile stations compatible with space division multiplexand mobile stations uncompatible therewith. Meanwhile, SDMA, when toimplement, usually employs space division based on directive beams. Incase SDM is done furthermore, beam-to-beam spatial correlation isincreased resulting in a propagation condition not suited for SDM ingeneral cases.

DISCLOSURE OF THE INVENTION

A radio communication system of the present invention is characterizedto implement space division multiplex transmission and space divisionmultiple access by use of a predetermined space division multiplextransmission evaluation criterion and space-division-multiple-accessevaluation criterion in an environment that there are coexisting a basestation having a plurality of antennas and capable of adaptivelychanging the directionality, space-division-multiplex compatible mobilestations that are compatible with space division multiplex transmissionand space-division-multiplex uncompatible mobile stations that areuncompatible with space division multiplex transmission, within acommunication area.

Meanwhile, a radio communication system of the invention comprises: aspace-division-multiplex compatible mobile station compatible with spacedivision multiplex transmission; a space-division-multiplex uncompatiblemobile station uncompatible with space division multiplex transmission;and a base station including partial-space orthogonalizing means formaking a weighting process, for enhancing orthogonality over apropagation path for the space division multiplex transmission, on atransmission data sequence to be sent by space division multiplex to thespace-division-multiplex compatible mobile station allocated for spacedivision multiplex transmission within a communication area, a beamforming section for forming a transmission beam to thespace-division-multiplex compatible mobile station and thespace-division-multiple-access mobile station, responsive to atransmission data sequence to the space-division-multiple-access mobilestation allocated for space division multiple access within acommunication area and to an output of the partial-space orthogonizingmeans, the transmission beam being to reduce an interference withanother mobile station to access simultaneously, and a plurality ofantennas for transmitting the transmission beam.

Meanwhile, forming the transmission beam for reducing an interference bythe beam forming section of the base station apparatus in the radiocommunication system of the invention is to form the transmission beamfrom the transmission data sequence to the allocatedspace-division-multiple-access mobile station and an output of thepartial-space orthogonalizing means in a manner being orthogonal to achannel estimation matrix on another mobile station to accesssimultaneously.

This allows for implementing space division multiplex transmission andspace division multiple access at the same time and for selecting amobile station with which multiplexing is available with use of a spacedomain, hence having a function to efficiently make use of spacedivision multiplex.

A radio communication method of the invention comprises: a step forallowing a base station apparatus to calculate a space divisionmultiplex transmission evaluation criterion andspace-division-multiple-access evaluation criterion, on a basis of achannel estimation matrix and received quality for aspace-division-multiplex compatible mobile station andspace-division-multiplex uncompatible mobile station; a step forallowing the base station apparatus to allocate thespace-division-multiplex compatible mobile station to space divisionmultiplex transmission by the space division multiplex transmissionevaluation criterion and make a weighting process for an enhancement oforthogonality over a propagation path for the space division multiplextransmission, on a transmission data sequence to be sent by spacedivision multiplex to the allocated space-division-multiplex compatiblemobile station; and a step for allowing the base station apparatus toassign the space-division-multiplex compatible mobile station andspace-division-multiplex uncompatible mobile station to space divisionmultiple access by the space-division-multiple-access evaluationcriterion, and form a transmission beam to the space-division-multiplexcompatible mobile station and space-division-multiple-access mobilestation responsive to a transmission data sequence to the allocatedspace-division-multiple-access mobile station and the transmission datasequence weighting-processed and to be sent by space division multiplex,the transmission beam being to reduce an interference with anothermobile station to access simultaneously, thus sending same from thebase-station antenna.

Meanwhile, a radio communication method according to the inventionfurther comprises a step for allowing the base station apparatus to sendknown signals on each of antennas provided in a number of N, a step forallowing the space-division-multiplex compatible mobile station andspace-division-multiplex uncompatible mobile station to measure, on eachof antennas provided in a total number of M, a channel estimation matrixconstituted by channel estimation values in a number of N×M by use of areceived result of the known signals in a number of N, and further tomeasure a received quality, and a step for allowing thespace-division-multiplex compatible mobile station andspace-division-multiplex uncompatible mobile station to send the channelestimation matrix and received quality to the base-station apparatusthrough a communication line, wherein, forming the transmission beam forreducing an interference by the base station apparatus is to form thetransmission beam from a transmission data sequence to thespace-division-multiple-access mobile station allocated and atransmission data sequence weight-processed and to be sent by spacedivision multiplex, in a manner being orthogonal to a channel estimationmatrix on another mobile station to access simultaneously.

This enables to decide the applicability of space division multiplextransmission and space division multiple access, depending upon achannel estimation value and received quality information.

Meanwhile, a radio communication method according to the invention ischaracterized in that the known signal is to be sent by time divisionmultiplex on an antenna-by-antenna basis by use of different codesequences from base-station antennas in the number of N, thus having afunction to measure at the base station a channel estimation value oneach of the base-station antennas.

Meanwhile, a radio communication method according to the invention ischaracterized in that the known signal is sent by code divisionmultiplex on an antenna-by-antenna basis by use of different codesequences from base-station antennas in the number of N, thus having afunction to measure at the base station a channel estimation value oneach of the base-station antennas.

Meanwhile, a radio communication method according to the invention ischaracterized in that the known signal is to be sent by a combination oftime division multiplex and code division multiplex on anantenna-by-antenna basis by use of different code sequences frombase-station antennas in the number of N, thus having a function tomeasure at the base station a channel estimation value on each of thebase-station antennas.

Meanwhile, a radio communication method of the invention comprises: astep for allowing the space-division-multiplex compatible mobile stationand space-division-multiplex uncompatible mobile station to send knownsignals to a base station at each of antennas provided thereon in atotal number of M; a step for allowing the base station to receive ateach of a plurality N of base-station antennas and measure a channelestimation matrix constituted by channel estimation values in a numberof N×M depending upon the known signal, and further to measure areceived quality; a step for allowing the base station to calculate aspace division multiplex transmission estimating criterion andspace-division-multiple-access estimating criterion depending upon thechannel estimation matrix and the received quality; a step for allowingthe base station apparatus to allocate the space-division-multiplexcompatible mobile station to space division multiplex transmission bythe space division multiplex transmission evaluation criterion and makea weighting process for an enhancement of orthogonality, over apropagation path for the space division multiplex transmission, on atransmission data sequence to be sent by space division multiplex to theallocated space-division-multiplex compatible mobile station; and a stepfor allowing the base station to allocate the space-division-multiplexcompatible mobile station and space-division-multiplex uncompatiblemobile station to space division multiple access by thespace-division-multiple-access evaluation criterion, and form atransmission beam to the space-division-multiplex compatible mobilestation and space-division-multiple-access mobile station responsive toa transmission data sequence to the allocatedspace-division-multiple-access mobile station and the transmission datasequence weighting-processed and to be sent by space division multiplex,the transmission beam being to reduce an interference with anothermobile station to access simultaneously, thus transmitting thetransmission beam from the base-station antenna. This enables thedecision for applicability of space division multiplex transmission andspace division multiple access, depending upon a channel estimationvalue and received quality information.

Meanwhile, forming the transmission beam for reducing an interference bythe base station in a radio communication method according to theinvention is to form the transmission beam from a transmission datasequence to the allocated space-division-multiple-access mobile stationand a transmission data sequence weight-processed and to be sent byspace division multiplex, in a manner being orthogonal to a channelestimation matrix on another mobile station to access simultaneously.

Meanwhile, a radio communication method according to the invention ischaracterized in that the received quality uses any ofreceived-signal-power-to-noise-power ratio,received-signal-power-to-interference-power ratio and received power.This provides a function to grasp a received quality of in the mobilestation.

Meanwhile, a radio communication method according to the invention ischaracterized in that the received quality usesreceived-signal-power-to-noise-power ratio, and any one of moving speedof the mobile station and fading frequency estimation value, thusenabling to decide the applicability of space division multiplextransmission and space division multiple access in accordance with aroaming status of the mobile station.

Meanwhile, a radio communication method according to the invention ischaracterized in that the step of calculating a space division multiplextransmission estimating criterion comprises a step of selecting aspace-division-multiplex compatible mobile station satisfying apredetermined received quality, and a step of deciding a space divisionmultiplex transmission count depending upon a space correlationcoefficient of between channel estimation values in a number of Nobtained between different antennas on the space-division-multiplexcompatible mobile station of among selected ones of thespace-division-multiplex compatible mobile stations, thus enabling todecide the applicability of space division multiplex transmission andspace division multiple access in accordance with a propagationenvironment of the mobile station.

Meanwhile, a radio communication method according to the invention ischaracterized in that the base station embeds previously a known signalin a data sequence to be sent on a transmission beam to thespace-division-multiplex compatible mobile station or thespace-division-multiplex uncompatible mobile station that isspace-division-multiple accessed, and the space-division-multiplexcompatible mobile station space-division-multiple accessed calculates achannel estimation value depending upon the known signal and makesdemultiplex-receiving of a signal sent by space division multiplexdepending upon the channel estimation value, thus having a function todemultiplex-receive at the mobile station a pluralityspace-division-multiplex-transmission signalsspace-division-multiplex-transmitted.

Meanwhile, a radio communication method according to the invention ischaracterized in that the step of calculating aspace-division-multiple-access evaluation criterion comprises a step ofallocating the mobile station, with priority, by predeterminedscheduling means, a step of selecting a space-division-multiplexcompatible mobile station or space-division-multiplex uncompatiblemobile station satisfying a predetermined received quality from theothers than the mobile station allocated with priority, and a step ofselecting a mobile station having an antenna minimal in a spacecorrelation coefficient to a channel estimation matrix obtained at anantenna of the mobile station allocated with priority from amongselected ones of the space-division-multiplex compatible mobile stationsor space-division-multiplex uncompatible mobile stations, thus having afunction to select a mobile station with which space division multipleaccess is available with a predetermined communication quality.

Meanwhile, a radio communication method according to the invention ischaracterized in that the transmission beam for space division multipleaccess or space division multiplex transmission is placed under powercontrol into a predetermined communication quality. This provides afunction to enable communication at between the base station and themobile station with a predetermined communication quality.

Meanwhile, a radio communication method according to the invention ischaracterized in that power control is made to set a communicationquality of from the base station apparatus to thespace-division-multiplex uncompatible mobile station higher than acommunication quality of from the base station apparatus to thespace-division-multiplex compatible mobile station. This provides afunction to enhance, with priority, the received quality at thespace-division-multiplex uncompatible mobile station low in interferencesuppression performance, and thereby to compensate for it.

Meanwhile, a radio communication method according to the invention ischaracterized in that the space-division-multiple-access evaluationcriterion is to give priority to a multiple access of between thespace-division-multiplex uncompatible mobile stations in the case thatcall loss is greater than a predetermined value. This can increase thenumber of mobile stations with which simultaneous connections areavailable by giving priority to space division multiple access, thushaving a function to suppress call loss.

A base station apparatus of the invention comprises: a partial-spaceorthogonalizing means for making a weighting process, for enhancingorthogonality over a propagation path for the space division multiplextransmission, on a transmission data sequence to be sent by spacedivision multiplex to the space-division-multiplex compatible mobilestation allocated for space division multiplex transmission within acommunication area; a beam forming section for forming a transmissionbeam to the mobile station responsive to a transmission data sequence tothe space-division-multiple-access mobile station allocated for spacedivision multiple access within a communication area and an output ofthe partial-space orthogonizing means, the transmission beam to themobile station being to reduce an interference with another mobilestation to access simultaneously; and a plurality of antennas fortransmitting the transmission beam.

Meanwhile, a base station apparatus according to the invention ischaracterized in that forming the transmission beam for reducing aninterference by the beam forming section is to form the transmissionbeam from the transmission data sequence to the allocatedspace-division-multiple-access mobile station and the output of thepartial-space orthogonizing means, in a manner being orthogonal to achannel estimation matrix on another mobile station to accesssimultaneously. This provides a function to form a transmission beam towhich space division multiplex transmission and space division multipleaccess are to be applied simultaneously.

Meanwhile, in the weighting process in the beam forming section of thebase station apparatus of the invention, in a case that thespace-division-multiplex compatible mobile station and thespace-division-multiplex uncompatible mobile station are allocated forspace division multiple access at a same time, the beam forming sectionmakes, for the space-division-multiplex uncompatible mobile station, amaximum ratio synthetic beam as a transmission beam to thespace-division-multiplex uncompatible mobile station and, for thespace-division-multiplex compatible mobile station, a transmission beamas a beam for reducing an interference with another of thespace-division-multiplex uncompatible mobile station andspace-division-multiplex compatible mobile station to accesssimultaneously, whereby transmission is made possible that the receivedquality at the space division multiplex compatible mobile station nothaving a spatial interference suppression ability is enhanced withpriority rather than the space-division multiplex mobile station.

Meanwhile, forming the transmission beam for reducing an interference bythe beam forming section of the base station apparatus of the inventionis to form the transmission beam orthogonal to a channel estimationmatrix on another of the space-division-multiplex uncompatible mobilestation and space-division-multiplex compatible mobile station to accesssimultaneously.

Meanwhile, a base station apparatus according to the invention furthercomprises space-time coding means for making a space-time coding processon a transmission data sequence to the space-division-multiplexcompatible mobile station, the transmission data sequence space-timecoded being outputted to the partial-space orthogonizing means. This canimprove the received quality due to addition of the error correctionability added with a transmission diversity effect despite transmissionrate lowers.

Meanwhile, a base station apparatus according to the invention furthercomprises a deciding section for allocating thespace-division-multiple-access mobile station and thespace-division-multiplex mobile station by use of a predetermined spacedivision multiplex transmission evaluation criterion andspace-division-multiple-access evaluation criterion. This enables todecide the applicability of space division multiplex transmission andspace division multiple access.

Meanwhile, a base station apparatus according to the invention ischaracterized in that the space division multiplex transmissionevaluation criterion and the space-division-multiple-access evaluationcriterion are to be calculated depending upon a channel estimation valueand received quality received from the mobile station of within thecommunication area. This enables to decide the applicability of spacedivision multiplex transmission and space division multiple access,depending upon a channel estimation value and received qualityinformation.

Meanwhile, a base station apparatus according to the invention ischaracterized in that, in a case that the space-division-multiple-accessmobile stations include a space-division-multiplex compatible mobilestation and a space-division-multiplex uncompatible mobile station, atransmission beam to the space-division-multiplex uncompatible mobilestation is formed by use of a complex-conjugate-transposition of achannel estimation matrix on the space-division-multiplex uncompatiblemobile station, and a transmission beam to the space-division-multiplexcompatible mobile station is formed in a manner being orthogonal to achannel estimation matrix on another space-division-multiple-accessmobile stations to access simultaneously. This enables thespace-division-multiplex uncompatible mobile station to gain a receivedsignal that a plurality of transmission signals from a plurality ofantennas of the base station are synthesized in maximal ratio.

As described above, according to the present invention, there isprovided a radio communication system allowed for space divisionmultiplex transmission to particular mobile stations as well as spacedivision multiple access to other mobile stations in a radiocommunication system having a base station having a plurality ofantennas, thus efficiently utilizing the spatial freedom at the basestation and improving the communication capacity over the radiocommunication system.

Meanwhile, by providing a control method for adaptively changing thespace division multiplex method (SDM, SDMA) depending upon a trafficstatus, etc. of within a communication area, communication capacity isimproved for the radio communication system through the effectiveutilization of SDM- or SDMA-based space division multiplex technique anduser diversity effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figure showing an arrangement of a radio communicationsystem in embodiment 1 of the present invention.

FIG. 2 is a figure showing a configuration of abase station and mobilestation in embodiment 1 of the invention.

FIG. 3A is a flowchart showing a mobile-station allocation processprocedure at the base station in embodiment 1 of the invention.

FIG. 3B is a flowchart showing a allocation process procedure at themobile station end in embodiment 1 of the invention.

FIG. 4A is a figure showing a frame structure in time divisiontransmission of an antenna-based pilot signal in embodiment 1 of theinvention.

FIG. 4B is a figure showing a frame structure in code divisiontransmission of an antenna-based pilot signal in embodiment 1 of theinvention.

FIG. 4C is a figure showing a frame structure in time/code divisiontransmission of an antenna-based pilot signal in embodiment 1 of theinvention.

FIG. 5A is a figure showing a frame structure in time divisiontransmission of a space-division-multiplex-channel-based pilot signal inembodiment 1 of the invention.

FIG. 5B is a figure showing a frame structure in code divisiontransmission of a space-division-multiplex-channel-based pilot signal inembodiment 1 of the invention.

FIG. 6 is a figure showing a configuration of abase station inembodiment 2 of the invention.

FIG. 7 is a figure showing a configuration of abase station and mobilestation in embodiment 3 of the invention.

FIG. 8 is a figure showing another configuration of a base station inembodiment 3 of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now an embodiment of the present invention will be explained with theuse of FIGS. 1 to 8.

Embodiment 1

FIG. 1 is a figure showing the outline of a radio communication systemaccording to embodiment 1 of the invention. Explained hereunder is amethod of communication using a space division multiplex in atransmission of from a base station to a mobile station (hereinafter,referred to as “downlink”).

In FIG. 1, a base station 1 has a plurality of antenna elements toadaptively vary the directivity of the antennas. SDM-compatible mobilestations 2-1-2 are a plurality of mobile stations compatible with spacedivision multiplex while SDM-uncompatible mobile stations 3-1-3 are aplurality of mobile stations uncompatible with SDM transmission.Transmission beams 4-1-4 are a plurality of beams of from the basestation 1 to the mobile stations to communicate. A communication area 5is an area in which the base station 1 is allowed to communicate withthe SDM-compatible mobile stations 2 and the SDM-uncompatible mobilestations 3. Incidentally, this is not limitative in respect of thenumber of SDM-compatible mobile stations 2 and the number ofSDM-uncompatible mobile stations 3.

When there are a plurality of communicatable SDM-compatible mobilestations 2 and SDM-uncompatible mobile stations 3 coexisting within thecommunication area 5, the radio communication system of the invention isallowed to make any one of or both simultaneously of a space divisionmultiple access to between different mobile stations and a spacedivision multiplex to the same one of the mobile stations. Thus, spacedivision multiplex is made feasible with efficiency. Note that theSDM-compatible mobile stations 2, or including SDM-uncompatible mobilestations 3, are hereinafter expressed as mobile stations MS_(m) withnumbering. Incidentally, m takes a natural number equal to or smallerthan the number of mobile stations N_(ms) within the communication area5. The base station 1 is to decide, from a multiplicity ofSDM-compatible mobile stations 2 and SDM-uncompatible mobile stations 3,whether both simultaneously of or any one of SDM and SDMA are available,thus forming a plurality of transmission beams 4 at the base stationantenna. This allows the base station 1 to realize space divisionmultiplex and space division multiple access as decided available.

FIG. 2 shows a detailed configuration of the base station BS and mobilestation MS in the radio communication system of the present embodiment.Incidentally, FIG. 2 shows the case to send an individual-usertransmission data sequence 211 to the SDM-compatible mobile station MS₁by use of two space division multiplex channels (SCH1, SCH2) as well asan individual-user transmission data sequence 212 to theSDM-uncompatible mobile station MS₂ by use of one space divisionmultiplex channel (SCH3). However, this is not limitative.

In the base station BS in FIG. 2, space-division multiplex transmissionevaluation criterion calculating means 201 is to calculate an evaluationcriterion for deciding whether suited for space division multiplextransmission. Space-division-multiple-access evaluation criterioncalculating means 202 is to calculate an evaluation criterion fordeciding whether suited for space division multiple access. By use ofthose evaluation criterion values, deciding means 203 is to decide anallocation of mobile stations to which SDM or SDMA is to be made.Meanwhile, weight generating means 204 is to generate a weight forforming a directivity suited for a propagation path, depending upon anoutput of the deciding means 203. Space-division-multiple-access controlmeans 205 is to make an output control of a transmission data sequencefor a desired mobile station, depending upon an output of the decidingmeans 203. Here, output control is to be effected, as an example, on thetransmission-data sequence 211 to the mobile station MS₁ and on thetransmission data sequence 212 to a mobile station MS₂.Space-division-multiplex transmission control means 16 is to make acontrol for space division multiplex transmission to a desired mobilestation, depending upon an output of the deciding means 203. Here,control is effected, as an example, for space division multiplex on thetransmission data sequence 211 to the SDM-compatible mobile station MS₁.Meanwhile, space-division-multiplex transmission control means 206 ismade by series-parallel converting means 209 for generating, as to onetransmission data sequence, a plurality of transmission data sequencecommensurate with space division multiplex count, and partial spaceorthogonalizing means 210 for sending, by spatially orthogonalizing, thetransmission data sequence series-parallel-converted (showing a casewith two space division multiplex channels (SCH1, SCH2) in the figure).

Meanwhile, beam forming section 207 is to multiply transmission weightsW₁-W₃ respectively on the space division multiplex channels SCH1-SCH3. Abase-station antenna 208 is made up by a plurality Nt (Nt>1) of antennaelements. Incidentally, the transmission weight W_(j) is constituted bya column vector having elements (complex number values) in the number ofantenna elements Nt.

Now explanation is made on the configuration of the SDM-compatiblemobile station MS₁.

A plurality Ns⁽¹⁾ of antennas 221 are provided on the mobile station MS₁to receive a radio-frequency signal sent from the base station BS. Areceiver section 222 is to convert the radio-frequency signal into abase-band signal. Space division demultiplex means 223 is todemultiplex-receive a space division multiplex signal out of thebase-band signal. Data mixing means 224 is to mix together the signalsdemultiplex-received, and restore them into the former data sequencetransmitted. A received data sequence 225 is to be outputted from thedata mixing means 224.

Now explanation is made on the SDM-uncompatible mobile station MS2.

A mobile station antenna 231 is provided on the mobile station MS₂ toreceive a radio-frequency signal sent from the base station BS. Areceiver section 232 is to output an MS₂ received data sequence 233 outof the radio-frequency signal.

Now explanation is made on the communicating operation of between thebase station 1 and the mobile stations MS_(m) in the present embodiment.FIG. 3 is a flowchart showing a process procedure for communicationallocation to the base station 1 and mobile stations MS_(m). Afterestablishing a frame synchronization and symbol synchronization, thebase station 1 having antenna elements and transmission systems in thenumber of Nt first sends, from the respective transmissing systems, aknown signal sequence (hereinafter, referred to as “antenna-based pilotsignals APk(t)”) comprising a predetermined symbol number Np (stepS301). Note that k is a transmission-system number wherein k=1, 2, . . ., Nt. Meanwhile, t=1, . . . , Np. Incidentally, where the base station 1has a sufficiently great number of antenna elements Nt or where the SDMspace division multiplex count is limited smaller than the number ofantenna elements Nt at the base station 1, there is no need to use allthe transmission systems in the number of Nt. Part of them may be usedto send antenna-based pilot signals.

Here, FIGS. 4A-C are figures showing the transmission timing ofantenna-based pilot signals (frame structure). FIG. 4A illustrates timedivision transmission by a deviation in transmission timing of a knownsignal sequence A (401) as antenna-based pilot signals, on anantenna-by-antenna basis. Incidentally, there is shown that theantenna-based pilot signals use the same pattern or mutually-orthogonalcode sequence based on PN signals, etc. FIG. 4B illustrates codedivision multiplex transmission at different antennas by use of a knowncode sequence B_(k) (402) orthogonal one to another. FIG. 4C illustratesa scheme in combination of time division transmission and code divisiontransmission. Namely, for a certain combination of antennas, timedivision slots at the same time are shared to send respectiveantenna-based pilot signals A1 (403), A2 (404) by code divisionmultiplex with the use of code sequences orthogonal one to another. Thiscan reduce the overhead in time division transmission where the numberof antennas is great at the base station 1. Meanwhile, it is possible tomoderate the reduction in orthogonality over a propagation path duringcode division multiplex.

Meanwhile, the mobile station MS_(m) existing within the communicationarea 5 demultiplex-receives the antenna-based pilot signal AP_(k)(t)sent on an antenna-by-antenna basis of the base station, and calculatesa channel estimation value (step S321). Furthermore, it measures aquality of reception (step S322).

Now explanation is made on the operation at the steps S321 and S322. Them-th mobile station MS_(m) existing within the communication area 5 hasantennas in the number of Ns(m) and reception systems in the number ofNs(m), thus enabling SDM-reception at space division multiplex channelsin the number of maximally Ns(m). Note that m is a natural number equalto or smaller than the number of mobile stations N_(ms) present withinthe communication area 5. Here, Ns(m)=1 is given for theSDM-uncompatible mobile station 3 while Ns(m)>1 is for theSDM-compatible mobile station 2. The mobile station MS_(m) makes acorrelation operation on r_(j,k) ^((m))(t) (j=1, . . . , Ns(m)) as aresult of reception of a k-th antenna-based pilot signal AP_(k)(t) atthe j-th antenna and reception system with AP_(k)(t) generated in themobile station MS_(m), and calculates a propagation-path channelestimation value h^(m)(j, k) as shown in (Equation 1). Incidentally, *is an operator for complex conjugate. Incidentally, the correlationoperation may be by saving a received result of antenna-based pilotsignals AP_(k)(t) in a plurality of number of times and making anaveraging process over those. In such a case, in case the mobile stationis at a sufficiently low speed of movement, the effect of noise can bereduced to possibly enhance the quality of channel estimation. Finally,the channel estimation values on the m-th mobile station MS_(m) are tobe calculated totally in the number of (the number of antenna-basedpilot signals Nt)×(the number of mobile-station antennas Ns(m)).

$\begin{matrix}{{h^{m}\left( {j,k} \right)} = {\sum\limits_{t = 1}^{Np}{{{AP}_{k}^{*}(t)}{r_{j,k}^{(m)}(t)}}}} & (1)\end{matrix}$

Subsequently, a received quality P^(m)(j, k) is calculated for eachantenna-based pilot signal and on each mobile-station antenna. Forreceived quality, it is possible to apply received signal power, SIR(signal power to interference power ratio), SNR (signal power to noisepower ratio), etc. In the below is shown an example using SNR. In thecase to estimate an SNR by use of an antenna-based pilot signalAP_(k)(t), signal power is taken as S^(m)(j, k)=|h^(m)(j, k)|²/Np.Received quality Pm(j, k), i.e. SNR (=S^(m)(j, k)/N^(m)(j, k)) can beevaluated by use of the noise power N^(m)(j, k) shown in (Equation 2).

$\begin{matrix}{{N^{m}\left( {j,k} \right)} = {\frac{1}{Np}{\sum\limits_{t = 1}^{Np}{{{r_{j,k}^{(m)}(t)} - {S^{m}\left( {j,k} \right)}}}^{2}}}} & (2)\end{matrix}$

The above corresponds to the operation at steps S321 and S322.

Then, the mobile station MS_(m) feeds the calculated channel estimationvalue h^(m)(j, k) and received quality P^(m)(j, k) back to the basestation 1 through a communication channel (step S323). Incidentally, asfor received quality, it is possible to feed an average of Ps (m) shownin (Equation 3) taken over the number of base-station antennas Nt andthe number of mobile-station antennas Ns (m) back to the base station 1through the communication channel in order to diminish the feedbackinformation, instead of feeding back all of (the number of antenna-basedpilot signals Nt)×(the number of mobile station antennas Ns (m)). Thebelow explains a scheme to convey Ps(m) as a received quality.Incidentally, although average value is calculated here over thereceived qualities Pm(j, k) as shown in (Equation 3), median or maximumvalue may be employed. In order to further diminish the amount offeedback information, the base station and the mobile station may sharea table whose channel estimation values h^(m)(j, k) and receivedqualities P^(m)(j, k) are quantized at a predetermined interval, tothereby exchange its table number.

$\begin{matrix}{{P_{s}(m)} = {\frac{1}{N_{t}{N_{s}(m)}}{\sum\limits_{k = 1}^{Nt}{\sum\limits_{j = 1}^{{Ns}{(m)}}{P^{m}\left( {j,k} \right)}}}}} & (3)\end{matrix}$

Meanwhile, in the base station 1, it is checked whether or not thespace-division-multiplex-transmission evaluation criterion calculatingmeans 201 and space-division-multiple-access evaluation criterioncalculating means 202 received feedback information about a channelestimation value h^(m)(j, k) and received quality information Ps(m) 213(step S302). When received, the deciding means 203 decides apreferentially-allocated mobile station depending upon an output resultcalculated from them (step S303). The scheduling method forpreferentially allocating a mobile station includes a maximum CIRmethod, a proportional fairness method and the like that are packetscheduling based on SIR, which are disclosed of information in DocumentA. Jalali et al, “Data Throughput of CDMA-HDR a High Efficiency-HighData Rate Personal Communication Wireless System,” IEEE VTC2000-Spring,pp. 1854-1858. It is assumed here that the A-th mobile station MS_(A) ispreferentially allocated to commence mobile-station-based (user-based)communication.

Then, the deciding means 203 of the base station 1 decides whether ornot SDM transmission is available with the preferentially-allocatedmobile station MSA depending upon an evaluation value calculated by thespace-division-multiplex-transmission evaluation criterion calculatingmeans 201 (step S304). In case it is an SDM-uncompatible mobile station3, the deciding means 203 searches for a mobile station to which SDMA isavailable (step S306).

Meanwhile, in case it is an SDMA-compatible mobile station 2, anSDM-compatible process is made (step S305) by using the fed backpropagation-path channel estimation value h^(A) (j, k). Subsequently,searched for is a mobile station with which SDMA is available (stepS306). Note that k=1, . . . , Nt while j=1, . . . , Ns(A). It is assumedthat space-division-multiplex channels are used in the number of Nc as aresult of decision. Note that it is a natural number satisfying1≦Nc<Ns(A). Here, in the SDM-compatible process, the channel estimationvalues h^(A)(j, k) concerning the mobile station MSA can be expressed asa matrix as in (Equation 4), to calculate singular values λj in thenumber of Ns(A) obtainable by singular value resolution of H(A) wherebythe number of space division multiplex channels can be decided due tothe number of the singular values exceeding a predetermined value. Here,j=1, . . . , Ns(A). Meanwhile, calculation can be made, as anothermethod, for correlation coefficients at between row vectors in thenumber of (Ns(A)−1) of H(A) (hereinafter, spatial correlationcoefficients), to take a number assuming equal to or smaller than apredetermined value as the number of space division multiplex channels.

$\begin{matrix}{{H(A)} = \begin{bmatrix}{h^{A}\left( {1,1} \right)} & {h^{A}\left( {1,2} \right)} & \ldots & {h^{A}\left( {1,N_{t}} \right)} \\{h^{A}\left( {2,1} \right)} & {h^{A}\left( {2,2} \right)} & \ldots & {h^{A}\left( {2,N_{t}} \right)} \\\vdots & \vdots & \vdots & \vdots \\{h^{A}\left( {{N_{s}(A)},1} \right)} & {h^{A}\left( {{N_{s}(A)},2} \right)} & \ldots & {h^{A}\left( {{N_{s}(A)},N_{t}} \right)}\end{bmatrix}} & (4)\end{matrix}$

Meanwhile, searching for an SDMA-available mobile station SDMA (stepS306) is based on a channel estimation value or received qualityinformation fed back to the base station 1. At first, by using thereceived quality information Ps(m) except for the received qualityinformation Ps(A) about the A-th mobile station MS_(A), a mobile stationhaving a quality exceeding a predetermined level is selected in thefirst stage. As predetermined level setting, setting may be asPs(m)>Ps(A)+C using a predetermined margin value C (where m represents amobile station number within the communication area 5, except for A).

In this case, selection is possible for a mobile station higher inreceived quality than the A-th mobile station MS_(A). In the case ofeffecting a transmission power control to the base station 1, thetransmission power from the base station 1 can be set lower than theA-th mobile station MS_(A), thus enabling to reduce the interferencewith the mobile station MS_(A).

Then, calculated is a spatial correlation coefficient SC(m, A) betweenthe channel estimation value h^(A)(j, k) on the already allocated mobilestation MSA and the channel estimation value h^(m)(j, k) among themobile stations selected in the first stage, by use of (Equation 5) or(Equation 6). Here, * represents a complex conjugate. Here, m representsa number of the mobile station selected in the first stage.

$\begin{matrix}{{{SC}\left( {m,A} \right)} = {\frac{1}{{N_{s}(m)}{N_{s}(A)}N_{t}}{\sum\limits_{j_{A} = 1}^{{Ns}{(A)}}{\sum\limits_{j_{m} = 1}^{{Ns}{(m)}}{\sum\limits_{k = 1}^{Nt}\frac{\left\lbrack {h^{m}\left( {j_{m},k} \right)} \right\rbrack^{*}{h^{A}\left( {j_{A},k} \right)}}{\sqrt{h^{m}\left( {j_{m},k} \right)}\sqrt{h^{A}\left( {j_{A},k} \right)}}}}}}} & (5) \\{{{SC}\left( {m,A} \right)} = {\max\limits_{{j_{A} \in {{Ns}{(A)}}},{j_{m} \in {{Ns}{(m)}}}}{\frac{1}{N_{t}}{\sum\limits_{k = 1}^{Nt}\frac{\left\lbrack {h^{m}\left( {j_{m},k} \right)} \right\rbrack^{*}{h^{A}\left( {j_{A},k} \right)}}{\sqrt{h^{m}\left( {j_{m},k} \right)}\sqrt{h^{A}\left( {j_{A},k} \right)}}}}}} & (6)\end{matrix}$

For all the subjects of mobile stations MS_(m) selected in the firststage, spatial correlation coefficient operation is made in thespace-division-multiple-access evaluation criterion calculating means202 according to (Equation 5) or (Equation 6), to decide whether or notthe mobile station MS_(m) lowest in spatial coefficient SC(m, A)relative to the A-th mobile station MS_(A) is below a predeterminedspatial correlation coefficient (step S307). When below, it is selectedas a space-division-multiple-access mobile station (assumably taken as aB-th mobile station) and furthermore it is determined whether thespace-division-multiple-access mobile station is an SDM-compatiblemobile station 2 or not (step S308). In case it is an SDM-uncompatiblemobile station 3, search is made again for a mobile station MS_(m) SDMAis available (step S306). In case it is an SDM-compatible mobile station2, SDM-compatible process is made using the similar method to the stepS305 by use of a channel estimation value h^(B)(j, k) over a propagationpath feedback has been made (step S309). Note that k=1, . . . , Nt whilej=1, . . . , Ns(B). It is assumed that space division multiplex channelsin the number of Nc^((B)) are assumably used as a result of decision.However, it is a natural number satisfying 1<Nc^((B))<Ns^((B)). Afterthe decision, search is made again for a mobile station MS_(m) SDMA isavailable (step S306).

Incidentally, when searching for a mobile station MS_(m) SDMA isavailable in the case a plurality of mobile stations MS_(m) have beenallocated in the step S306, MSC(m) shown in (Equation 7) is used inplace of SC(m, A). MSC(m) provides the maximum SC(m, k) for the alreadyallocated mobiles stations A, B, C, . . . . However, k provides a numberof the already allocated mobile station MS_(A), MS_(B), MS_(C), . . . .

$\begin{matrix}{{{MSC}(m)} = {\max\limits_{{k = A},B,C,\;\ldots}\mspace{11mu}{{SC}\left( {m,k} \right)}}} & (7)\end{matrix}$

Then, in the case of a determination at step S307 that there are nomobile stations MS_(m) SDMA is available, a communication startnotification including a notification (notifying the number of spacedivision multiplex ones) as to whether to carry out an SDM, to theallocated predetermined mobile station MS_(m) without effecting spacedivision multiple accesses furthermore (step S310).

Then, the base station starts an individual-user channel transmission tothe mobile station MS_(m) (step S311). Meanwhile, a predetermined mobilestation MS_(m), when receiving the communication start notification fromthe base station 1, makes a process for individual-user channelreception (step S324) and starts to receive the signals thereafter sentthrough the individual user channel (step S325). Incidentally, thetransmission power to the mobile stations MS_(m) allocated for SDMA areplaced under transmission power control to obtain a predeterminedreceived quality.

Incidentally, in the case of carrying out an SDMA at between theSDM-compatible mobile station 2 and the SDM-uncompatible mobile station3, the SDM-uncompatible mobile station 3 cannot be suppressed againstinterference in the space domain. Consequently, by setting a targetreceived quality higher to the SDM-uncompatible mobile station 3 thanthe SDM-compatible mobile station 2, received quality in SDMA can beassured.

As in the above, even where there are SDM-compatible mobile stations 2and SDM-uncompatible mobile stations 3 within the communication area 5,the mobile station MSm feeds a channel estimation value and receivedquality information back to the base station 1 by use of anantenna-based pilot signal whereby the base station 1 is allowed toselect a mobile station MS_(m) where multiplexing is available using aspace domain combined with both simultaneously or anyone of SDA andSDMA, thus enabling to efficiently utilize space division multiplex.

Now explanation is made on the directivity control operation at themobile station MS and base station BS after completing the communicationallocation process.

The transmission data sequence is assumably S_(k) ^(n)(t) (where trepresents a time) which is on the k-th space division multiplex channelto the n-th mobile station MS_(n). Here, n is a natural number equal toor smaller than the number of mobile stations Nd to which space divisionmultiple access is to be made while k is a natural number equal to orsmaller than the number of space division multiplex ones Nc^((n)) to then-th mobile station MS_(n). Meanwhile, 1≦Nc^((n))<Ns⁽¹⁾. The channelestimation value is assumed h^(n)(p, m) which is received at the p-thantenna of the n-th mobile station MS_(n). The channel estimation valueh^(n)(p, m) is for the antenna-based pilot signal AP_(m)(t) of from them-th base-station antenna fed back from the mobile station MS_(n) to thebase station BS. Incidentally, m is a natural number equal to or smallerthan the number of base-station antennas Nt while p is a natural numberequal to or smaller than the number of antennas Ns^((n)) on the n-thmobile station MS_(n). Here, the channel estimation matrix H^(n) for then-th mobile station MS_(n) is defined as in (Equation 8).

$\begin{matrix}{H^{n} = \begin{bmatrix}{h^{n}\left( {1,1} \right)} & {h^{n}\left( {1,2} \right)} & \ldots & {h^{n}\left( {1,N_{t}} \right)} \\{h^{n}\left( {2,1} \right)} & {h^{n}\left( {2,2} \right)} & \ldots & {h^{n}\left( {2,N_{t}} \right)} \\\vdots & \vdots & \vdots & \vdots \\{h^{n}\left( {N_{s}^{(n)},1} \right)} & {h^{n}\left( {N_{s}^{(n)},2} \right)} & \ldots & {h^{n}\left( {N_{s}^{(n)},N_{t}} \right)}\end{bmatrix}} & (8)\end{matrix}$

In FIG. 2, the weight generating means 204 generates a transmissionweight by use of the channel estimation matrix H^(n) shown in (Equation8). Here, the transmission weight vector Wj for the j-th space divisionmultiplex channel is to form a beam not to cause interference with theother user n, SDMA is to be made, than j-th one. n is a natural numberequal to or smaller than the total number Nd of the mobile stations,SDMA is to be made, except for j-th one. Meanwhile, in the case thatallocation is only to the n-th mobile station MSn wherein SDMA is not tobe made, when the number of space division multiplex ones at that mobilestation is Nc^((n)), antennas in the number of Nc^((n)) are selected outof the base-station antennas 208, thereby effecting transmission.H ^(n) W _(j)=0,(j≠n)  (9)

Incidentally, (Equation 9) uses an orthogonal condition under whichtransmission signals are free from interference between the mobilestations. Besides, usable is a weight generating method based on minimummean square error (MMSE) as shown in (Equation 10). Here, Y_(nj) is asignal component of the transmission signal to the j-th mobile stationMS_(j) to be received by the n-th mobile station MS_(n).

$\begin{matrix}{{W_{j} = {\arg\mspace{14mu}{\min\limits_{W}{{y_{nj} - {H^{n}W}}}^{2}}}},\left( {j \neq n} \right)} & (10)\end{matrix}$

The beam forming section 207 duplicates the transmission data sequenceSCH^((j)) of j-th space division multiplex channel by the number of thebase-station antennas (Nt) by the use of transmission weight vectorsW^(j)=[W_(j1), W_(j2), . . . , W_(jNt)]^(T) (where j is a natural numberequal to or smaller than the total number Tc of the space divisionmultiplex channels, and T represents a vector transposition) in thenumber equal to the total number of the space division multiplexchannels Tc for use in SDM and SDMA, and multiplies thereon the elementsof the transmission weight vectors, thus sending it at the base-stationantenna 208.

As in the above, by generating transmission weights W_(j) satisfying(Equation 9), reception is at a channel estimation value CA to beexpressed as in (Equation 11) provided that W_(j) is the transmissionweight directed to the A-th mobile station MSA having the number ofspace division multiplex channels of Nc^((A))=1. Meanwhile, where W_(j),W_(j+1) and W_(j+Nc(B)−1) are the transmission weights directed to theB-th mobile station MS_(B) having the number of space division multiplexchannels of Nc^((B))>1, reception is at a channel estimation matrix CBin a degree of (Ns^((B))×Nc^((B))) to be expressed as (Equation 12).

In case the partial-space orthogonizing means 210 has transmissionweights W_(j), W_(j+1) and W_(j+NC(B)−1) directed to the B-th mobilestation MS_(B) having the number of space division multiplex channels ofNc^((B))>1 where to make an SDM-transmission to the B-th mobile stationMS_(B), reception is at a channel estimation matrix C_(B) in a degree of(Ns^((B))×Nc^((B))) to be expressed as (Equation 12). Meanwhile, itpreviously singular-value-resolves C_(B) as shown in (Equation 13), toselect the number Nc^((B)) of singular values in the greater order ofsingular values obtained. By using right singular-valued matrix Vs=[V₁,V₂, . . . , V_(NC(B))] constituted by the right singular value vectorscorresponding to those singular values λ_(k), the right singular-valuedmatrix Vs is multiplied from left on the space division multiplexchannel data sequence S(t)=[S₁ ^(B)(t) S₂ ^(B)(t) . . . SN_(c(B))^(B)(t)]^(T) as shown in (Equation 14), thereby calculating a signalsequence S₂(t). Here, k=1−Nc^((B)). The beam forming section 207multiplies the transmission weights W_(j), W_(j+1) and W_(j+Nc(B)−1)respectively on the elements of S₂(t) in the number of Nc^((B)). Here,in (Equation 13), U is a unitary matrix constituted by the left singularvalue vectors of the channel estimation matrix C_(B), V is a unitarymatrix constituted by the right singular value vectors of the channelestimation matrix C_(B), and Q is a diagonal matrix having diagonalcomponents as singular values.

Incidentally, the receiver section 222 can be configured by omitting thepartial-space orthogonizing means 210. In such a case, Vs in (Equation14) is given an Nc-degree unit matrix.

$\begin{matrix}{{H^{A}W_{j}} = C_{A}} & (11) \\{{H^{A}\left\lbrack {W_{j}W_{j + 1}\mspace{11mu}\ldots\mspace{11mu} W_{j + {{Nc}{(n)}} - 1}} \right\rbrack} = C_{B}} & (12) \\{C_{B} = {{U\;\Lambda\; V^{H}} = {{U\begin{bmatrix}Q & 0 \\0 & 0\end{bmatrix}}V^{H}}}} & (13) \\{{S_{2}(t)} = {V_{s}{S(t)}}} & (14)\end{matrix}$

The above is the operational explanation as to the base station 1.

Then, in order for the SDM-compatible mobile station MSn todemultiplex-receive the space division multiplex channels in the numberof Nc^((n)) and in order for the SDM-uncompatible mobile station MS_(n)to make a reception with synchronous detection, transmuission is made byembedding a known signal sequence (hereinafter,space-division-multiplex-channel-based pilot signals) CP_(k)(t) in eachspace division multiplex channel. Here, k is a natural number equal toor smaller than the total number of space division multiplex channelsTc. However, where the transmission signal is differentially coded anddelayed detection is applied, there is no need to send such aspace-division-multiplex-channel-based pilot signal.

FIGS. 5A and 5B shows a transmission method (frame structure) of aspace-division-multiplex-channel-based pilot signal CP_(k)(t). FIG. 5Ashows a method to send a space-division-multiplex-channel-based pilotsignal sequence A_(k) (501) by time division with a deviation oftransmission timing. The antenna-based pilot signals use the samepattern, or mutually-orthogonal code sequences based on PN (pseudorandom signals) signals, etc. FIG. 5B shows a method of sending by codedivision multiplex at different space division multiplex channels by theuse of space-division-multiplex-channel-based pilot signal sequencesB_(k) (502) as mutually-orthogonal code sequences. Meanwhile, it ispossible to use a method that time division transmission and codedivision transmission are combined together as explained in FIG. 4C.

Now explanation is made on the reception operation at the mobile stationMS, as for the n-th SDM-compatible mobile station MS_(n).

At first, the mobile-station antennas 221 in the number of Ns^((n))receive a space-division-multiplexed radio-frequency signal.

The receiver section 222 in the number of Ns^((n)) output complexbase-band signals r_(j) ^((n))(t) in the number of Ns^((n)) comprising Iand Q signals by orthogonal detection after frequency conversion, forthe received radio-frequency signals in the number of Ns^((n))respectively. (Note that j is a natural number equal to or smaller thanNs^((n))) Then, the space division demultiplex means 223 demultiplexesthe space division multiplex channels in the number of Nc^((n)) to theSDM-compatible mobile station MS_(n).

In the method of demultiplexing the space division multiplex channel, itis possible to apply such techniques as 1) a method of utilizing aninverse matrix to a channel estimation matrix (zero-forcing technique),2) maximum likelihood estimation (joint estimation), 3) V-BLAST and soon. In the below, explanation is on the operation using the method 1).

At first, by using the space-division-multiplex-channel-based pilotsignal CP_(k)(t) individually embedded in the space-division multiplexchannel, channel estimation values h^(n)(j, k) are calculated on eachspace-division multiplex channel as shown in (Equation 15). Here, k is anatural number equal to or smaller than the number of space divisionmultiplex channels Nc^((n)) to be sent to the SDM-compatible mobilestations MS_(n). Incidentally, * is a complex conjugate operator andwherein the space-division-multiplex-channel-based pilot signalCP_(k)(t) assumably has the number of symbols N_(q). For each spacedivision multiplex channel obtained, a channel estimation matrix H^(n)shown in (Equation 16) is generated having constituent elements ofchannel estimation values h^(n)(j, k). By multiplying the generalinverse matrix (H^(n))⁻¹ of the same on a reception signal vector R=[r₁^((n))(t), r₂ ^((n))(t), . . . , r_(Ns(n)) ^((n))(t)]^(T), therespective space division multiplex channels are demultiplex-received.Incidentally, concerning the number of space division multiplex ones andthe kind of the space-division-multiplex-channel-based pilot signal tothe mobile station MS_(n), notification is previously made from the basestation BS to the mobile station MS_(n) by way of the control channel,etc.

$\begin{matrix}{{h^{n}\left( {j,k} \right)} = {\sum\limits_{t = 1}^{Nq}{{{CP}_{k}^{*}(t)}{r_{j}^{(n)}(t)}}}} & (15) \\{H^{n} = \begin{bmatrix}{h^{n}\left( {1,1} \right)} & {h^{n}\left( {1,2} \right)} & \ldots & {h^{n}\left( {1,N_{c}^{(n)}} \right)} \\{h^{n}\left( {2,1} \right)} & {h^{n}\left( {2,2} \right)} & \ldots & {h^{n}\left( {2,N_{c}^{(n)}} \right)} \\\vdots & \vdots & \vdots & \vdots \\{h^{n}\left( {N_{s}^{(n)},1} \right)} & {h^{n}\left( {N_{s}^{(n)},2} \right)} & \ldots & {h^{n}\left( {N_{s}^{(n)},N_{c}^{(n)}} \right)}\end{bmatrix}} & (16)\end{matrix}$

Incidentally, there is a method as another method for space divisiondemultiplex that, when the partial space orthogonalizing means 210 isused in SDM transmission to the B-th mobile station MS_(B), singularvalues are selected Nc in the greater order of those obtained insingular value resolution of C_(B) as shown in (Equation 13). By usingaright singular-valued matrix Us=[U₁, U₂, . . . , U_(Nc(B))] constitutedby left singular-value vector corresponding to those singular values,whose complex-conjugate-interposed matrix (Us)H is multiplied from lefton the reception signal vector R=[r₁ ^((B))(t), r₂ ^((B))(t), . . . ,r_(Ns(B)) ^((B))(t)]^(T). With this method, the respective spacedivision multiplex channels can be demultiplex-received. In this case,the right singular-valued matrix Us is previously notified to the mobilestation MS_(B) via the communication line. In the case of using thismethod, there is a merit of no need of sending aspace-division-multiplex-channel-based pilot signal because propagationchannel variation is simultaneously compensated for. Incidentally, asfor the number of space division multiplex ones and the kind of thespace-division-multiplexed-channel-based pilot signal to the mobilestation MS_(n), notification is previously made from the base station BSto the mobile station MS_(n) by way of the control channel, etc.

Now explanation is made on the reception operation in theSDM-uncompatible mobile station MS₁.

The receiver section 222 suitably frequency-converts the radio-frequencysignal received at the antenna and makes a reception operation by use ofdelayed detection, semi-synchronous detection or synchronous detection.The received signal is code-decided and decoded by a not-shown decoder,to restore the user-transmitted data. Incidentally, the SDM-uncompatiblemobile station MS₁ is expected to increase in the same interference wavecomponent because of its space division multiple access. In order toremove interference, by mounting a multi-path interference cancelerdescribed in the document, etc. disclosed in Electronic InformationSociety technical Report RCS2000-134(2000) by Higuchi et al., the sameinterference component can be removed. The post-removal received signalis code-decided and decoded by the decoder section, to restore theuser-transmitted data thereby obtaining high-quality receptionperformance.

As discussed above, in the present embodiment, the base station BS makesan allocation of the mobile stations for transmission through acombination of SDM and SDMA while the mobile station implements atransmission-directivity control method and an in-mobile-station spacedivision demultiplex receiving method. This allows the base station tomake a space division multiple access to another mobile station inaccordance with a propagation environment, together with space divisionmultiplex transmission to a particular mobile station. This makes itpossible to efficiently utilize the spatial freedom at the base station,to effectively make use of the space division multiplex technique anduser-diversity effect based on SDM or SDMA, and to improve thecommunication capacity of a radio communication system.

Incidentally, the present embodiment can be applied similarly to a radiocommunication system of a multi-carrier transmission scheme. In thiscase, there is available 1) a method of making a similar operation toembodiment 1 by use of one of a plurality of sub-carriers (e.g. asub-carriers at around a center frequency, etc.) and forming onetransmission beam common to the sub-carriers, and 2) a method of makinga similar operation to embodiment 1, i.e. channel estimation valuecalculation and received quality estimation on asub-carrier-by-sub-carrier basis, to feed those pieces of informationback to the base station 1 thereby allocating mobile stations MS_(m) foreffecting SDM and SDMA depending upon a calculated spatial correlationcoefficient. Incidentally, during calculating a spatial correlationcoefficient, a spatial correlation coefficient is calculated on eachsub-carrier similarly to embodiment 1, to allocate mobile stationsMS_(m) by taking, as the final spatial correlation coefficient, arepresentative value such as an average or median thereof, a maximumvalue and a minimum value. Meanwhile, by a transmission-beam formingmethod for forming a transmission beam on each sub-carrier, the presentembodiment can be applied similarly.

Incidentally, in the present embodiment it is possible to changeadaptively the allocation process of mobile stations MS_(m) inaccordance with the traffic status of SDM or SDMA. Where a number ofmobile stations MS_(m) exist within the communication area 5 and callloss occurs more frequently than a predetermined level, the process toomit the SDM-compatible process (step S305, S309) in FIG. 3 can givepriority to the mobile-station allocation that SDMA is available ratherthan SDM. This can obtain an effect that can increase the number ofmobile stations that communications are possible at the same time.

Meanwhile, the allocation process of mobile stations MS_(m) can beadaptively changed in accordance with the magnitude of communicationarea 5 (or cell radius). In this case, in the case that generally thebase-station antenna has a height greater than the surrounding buildingsas in the macro-cell, there is a comparative increase in the percentageof the region where the sight in transmission and reception can besecured within the communicating area 5. Hence, it becomes under theenvironment of communications suited for SDMA rather than SDM. For thisreason, priority is given to the mobile-station allocation for SDMArather than that for SDM by the process to omit the SDM-compatibleprocess (step S305, S309) in FIG. 3.

Incidentally, although this embodiment explained the communicationmethod using space division multiplex in the transmission of from thebase station 1 to the mobile station MS_(m) (downlink), it can besimilarly applied to the transmission of from the mobile station MS_(m)to the base station 1 (uplink). In this case, antenna-based pilotsignals are sent to the base station 1 by time or code division based oneach antenna provided on the mobile station MS_(m) so that a channelestimation value and received quality can be calculated on eachantenna-based pilot signal in the base station 1. This allows SDM orSDMA allocation to the mobile stations MS_(m) by the similar operationto the explanation with FIG. 3, without using the feedback informationfrom the mobile stations MS_(m).

Incidentally, in the present embodiment, the channel estimation valueand received quality information in the transmission of from the basestation 1 to the mobile station MS_(m) (downlink) is fed back to thebase station 1 through the communication line. Because the radiocommunication system using TDD (time division duplex) uses the samefrequency as transmission medium, antenna-based pilot signals are sentby time or code division to the base station 1 on each of the antennasprovided on the mobile stations MS_(m). In the base station 1, channelestimation values and received qualities are calculated on therespective antenna-based pilot signals. This allows SDM or SDMAallocation to the mobile stations MS_(m) by the similar operation to thecommunication allocation process explained with FIG. 3, without usingthe feedback information from the mobile stations MS_(m). Meanwhile, thepresent embodiment can be applied similarly to a TDD uplink.

Incidentally, the evaluation values related to the mobility ofmobile-stations MS_(m), such as estimated roaming velocity of the mobilestation MS_(m) and Doppler-frequency estimation value, may be combinedas received quality information, besides the received quality such asSNR explained in the present embodiment. In this case, although delayoccurs due to received quality information feedback or SDMA or SDMAallocation process, operation is made available by adding the step S306in FIG. 3 with a decision operation that SDMA or SDM allocation processis not made to the mobility stations higher than a predeterminedmobility.

Embodiment 2

FIG. 6 is a diagram showing a configuration of a base station apparatusaccording to embodiment 2 of the invention. This embodiment explained aspatial-channel forming method for communication, with priority, withthe SDM-uncompatible mobile station, in a radio communication systemwhere SDM-compatible mobile stations and SDM-uncompatible mobilestations coexist within the area.

The base station BS shown in FIG. 6 is different in configuration inthat there are provided SDM-uncompatible-mobile-station weightgenerating means 601 and SDM-compatible-mobile-station weight generatingmeans in place of the weight generating means 204 in FIG. 2 used inembodiment 1, thereby being different in the method to generate atransmission beam. Explanation is made below mainly on the differentpart from embodiment 2, to omit the explanation as to the part similarto embodiment 1. Incidentally, the explanation is on a directivitycontrol method in the mobile station MS and base station BS of aftercommunication allocation process to the mobile stations MS by use ofspace division multiplex in the downlink.

The transmission data sequence is assumed S_(k) ^(n)(t) (where trepresents a time) which is for the k-th space division multiplexchannel to the n-th mobile station MS_(n). Here, n is a natural numberequal to or smaller than the number of mobile stations Nd to which spacedivision multiple access is to be made while k is a natural number equalto or smaller than the number of space division multiplex ones Nc^((n))to the mobile stations MS_(n). Meanwhile, 1≦Nc^((n))<Ns⁽¹⁾. The channelestimation value is assumed h^(n)(p, m) which is in the case ofreception at the p-th antenna on the n-th mobile station MS_(n). Thischannel estimation value h^(n)(p, m) is for the antenna-based pilotsignal AP_(m)(t) of from the base-station antenna 208 fed back from themobile station MS_(n) to the base station BS. Incidentally, m is anatural number equal to or smaller than the number of base stationantennas Nt while p is a natural number equal to or smaller than thenumber of antennas Ns^((n)) at the n-th mobile station MS_(n). Here, thechannel estimation matrix H^(n) for the n-th mobile station Ms_(n) isdefined as in (Equation 8).

SDM-uncompatible-mobile station weight generating means 601 generates atransmission weight vector Ws=(H^((s)))^(H) for the s-thSDM-uncompatible mobile station MS_(n) and outputs it to SDM-compatiblemobile station weight generating means 602. Note that ^(H) representscomplex conjugate transposition. Due to the transmission weight vectorWs, the s-th SDM-uncompatible mobile station MS_(s) obtains a receivedsignal that combined in the maximal ratio are a plurality oftransmission signals from a plurality of antennas of the base stationBS.

The SDM-compatible-mobile station weight generating means 602 generatesa beam that the transmission weight vector Wj for the j-th spacedivision multiplex channel to the SDM-compatible mobile station MSj doesnot cause interference with the other users n, SDMA is to be made, thanthe j-th one, as in (Equation 9). n is a natural number equal to orsmaller than the total number of mobile stations Nd to which SDMA is tobe made. Due to this, in the case the transmission weight is W_(j) whichis directed to the A-th mobile station MS_(A) having the number of spacedivision multiplex channels of NC^((A))=1, reception is at a channelestimation value C^(A) to be expressed as (Equation 10). Meanwhile,where the transmission weight is W_(j), W_(j)+1, W_(j+Nc(B)−1) which isdirected to the B-th mobile station MS_(B) having the number of spacedivision multiplex channels of NC^((B))>1, reception is at a channelestimation value C_(B) in the degree of (Ns^((B))×Nc^((B))) to beexpressed as (Equation 12). Here, in case the partial-spaceorthogonizing means 210 has transmission weights W_(j), W_(j+1) andW_(j+Nc(B)−1) directed to the B-th mobile station MS_(B) having thenumber of space division multiplex channels of NC^((B))>1 where to makean SDM-transmission to the mobile station MS_(B), reception is at achannel estimation value C_(B) in the degree of (Ns^((B))×Nc^((B))) tobe expressed as (Equation 12). C_(B) is previously resolved intosingular values as shown in (Equation 13), to select the number Nc^((B))of singular values in the greater order of those obtained. By use of aright singular-valued matrix Vs=[V₁, V₂, . . . , V_(Nc(B))] constitutedby right singular values corresponding to those singular values λ_(k),the right singular-valued matrix Vs is multiplied from left on the datasequence S(t)=[S₁ ^(B)(t) S₂ ^(B)(t) . . . S_(Nc(B)) ^(B)(t)]^(T) ofspace division multiplex channel as shown in (Equation 14), to calculatea signal sequence S₂(t). Here, k=1−Nc^((B)).

Then, the beam forming section 207 multiples the transmission weightsW_(j), W_(j+1) and W_(j+Nc(B)−1) respectively on the elements of S₂(t)in the number of Nc^((B)). Here, in (Equation 13), U is a unitary matrixconstituted by the left singular value vectors of the channel estimationmatrix C_(B), V is a unitary matrix constituted by the right singularvalue vectors of the channel estimation matrix C_(B), and Q is adiagonal matrix having diagonal components as singular values.Incidentally, the partial-space orthogonizing means 210 can bestructurally omitted, in which case Vs in (Equation 14) is given asNc-degree unit matrix.

The operation in the mobile station MS_(n) is similar to embodiment 1.

As discussed above, explanation was made on the radio communicationsystem using a method of forming a beam to SDM-uncompatible mobilestations different from embodiment 1, as to the case of transmissionthrough a combination of SDM and SDMA at the base station BS. Due to thepresent embodiment, the base station uses, for the SDM-uncompatiblemobile stations, a transmission beam from which can be obtained areceived signal combined in the maximum ratio of a plurality oftransmission signals of from a plurality of antennas. This enables SDMAin the state the received quality to the SDM-uncompatible mobilestations is sectured at a certain level. Meanwhile, although there is anincreasing interference with the SDM-compatible mobile stations, theSDM-compatible mobile station can remove the interference by use of aspace domain due to a plurality of antennas provided thereon, thus beinghigher in immunity to interference than the SDM-uncompatible mobilestation. Due to this, the radio communication system can put thedecrease of throughput to a small range.

Incidentally, the present embodiment can be applied similarly to amulti-carrier-schemed radio communication system. In this case, there isavailable 1) a method of making a similar operation to embodiment 1 byuse of one of a plurality of sub-carriers (e.g. a sub-carrier at arounda center frequency, etc.) and forming one transmission beam common tothe sub-carriers, and 2) a transmission beam forming method of making asimilar operation to embodiment 1 by use of a part or all of a pluralityof sub-carriers and forming transmission beams on asub-carrier-by-sub-carrier basis based on channel estimation values forthe antenna-based pilot signals of the respective sub-carriers.

Embodiment 3

FIG. 7 is a diagram showing a configuration of a base station apparatusaccording to embodiment 3 of the invention. This embodiment is differentfrom embodiment 1 in that space division multiplex transmission controlmeans 701 has space-time coding means 702 for making a space-time-codingat between the channels for space division multiplex transmission.

Explanation is made mainly on the part of the space division multiplexcontrol means 701 different from embodiment 1. Meanwhile, theexplanation is made, using FIG. 7, on a directivity control method inthe mobile station MS and base station BS of after communicationallocation process to the mobile stations MS by use of space divisionmultiplex in the downlink, similarly to embodiment 1.

The transmission data sequence is assumed S_(k) ^(n)(t) (where trepresents a time) which is on the k-th space division multiplex channelto the n-th mobile station MS_(n). Here, n is a natural number equal toor smaller than the number of mobile stations Nd to which space divisionmultiple access is to be made while k is a natural number equal to orsmaller than the number of space division multiplex ones Nc^((n)) to themobile stations MS_(n). Meanwhile, 1≦Nc^((n))<Ns⁽¹⁾. The channelestimation value is assumed h^(n)(p, m) which is in the case ofreception at the p-th antenna on the n-th mobile station MS_(n). Thischannel estimation value h^(n)(p, m) is for the antenna-based pilotsignal AP_(m)(t) of from the base-station antenna 208 fed back from themobile station MS_(n) to the base station BS. Incidentally, m is anatural number equal to or smaller than the number of base stationantennas Nt while p is a natural number equal to or smaller than thenumber of antennas Ns^((n)) at the n-th mobile station MS_(n). Here, thechannel estimation matrix H^(n) for the n-th mobile station Ms_(n) isdefined as in (Equation 8).

The space-time coding means 702 outputs aspace-division-multiplex-channel data sequence S(t)=[S₁ ^(B)(t) S₂^(B)(t) . . . S_(Nc(B)) ^(B(t)]) ^(T) which space-time coding process ismade on a transmission data sequence 211 to mobile station MS1, to whichspace division multiplex is to be made, of after being processed by anot shown predetermined error-correction coding process, interleaveprocess and symbol-mapping process onto a modulation-phase plane.Concerning space-time coding and a decoding method thereof, there areinformation-disclosed of the techniques including STBC (Space-Time BlockCoding), STTC (Space-Time Trellis Coding) and ST Turbo TC (Space-TimeTurbo Trellis Codes), in B. Vucetic, J. Yuan, “Space-Time Coding”, J.Wiley & Sons Ltd (2003), which is omitted to explain here. By making aspace-time coding, transmission rate lowers. However, reception-qualityimprovement effect can be obtained due to diversity effect.

In the case the partial-space orthogoniizing means 210 has transmissionweights W_(j), W_(j+1) and W_(j+Nc(B)−1) directed to the B-th mobilestation MS_(B) having the number of space division multiplex channels ofNc^((B))>1 where to make an SDM-transmission to the B-th mobile stationsMS_(B), reception is at a channel estimation matrix C_(B) in a degree of(Ns^((B))×Nc^((B))) to be expressed as (Equation 12). It previouslysingular-value-resolves C_(B) as shown in (Equation 13), to select thenumber Nc^((B)) of singular values in the greater order of thoseobtained. By using right singular-valued matrix Vs=[V₁, V₂, . . . ,V_(Nc(B))] constituted by the right singular value vectors correspondingto those singular values λ_(k), the right singular-valued matrix Vs ismultiplied from left on the space-division-multiplex-channel datasequence S(t)=[S₁ ^(B)(t) S₂ ^(B)(t) . . . S_(Nc(B)) ^(B)(t)]^(T) asshown in (Equation 14), thereby calculating a signal sequence S₂(t).Here, k=1−Nc^((B)).

Incidentally, the partial-space orthogonizing means 210 can bestructurally omitted, in which case Vs in (Equation 14) is given asNc-degree unit matrix. Accordingly, in this case, the configuration isof the space division multiplex transmission control means 801 as shownin FIG. 8.

Then, the beam forming section 207 multiples the transmission weightsW_(j), W_(j+1) and W_(j+Nc(B)−1) obtained by the similar operation toembodiment 1 in the weight generating means 204, on the elements ofS₂(t) in the number of Nc^((B)). Here, in (Equation 13), U is a unitarymatrix constituted by the left singular value vectors of the channelestimation matrix C_(B), V is a unitary matrix constituted by the rightsingular value vectors of the channel estimation matrix C_(B), and Q isa diagonal matrix having diagonal components as singular values.

Meanwhile, in order for the SDM-compatible mobile station MSn todemultiplex-receive the space division multiplex channels in the numberof Nc^((n)) and in order for the SDM-uncompatible mobile station MSn tomake a reception with synchronous detection, transmission is made byembedding a known signal sequence (hereinafter,space-division-multiplexed-channel-based pilot signals) CP_(k)(t) ineach space division multiplex channel. Here, k is a natural number equalto or smaller than the total number Tc of space division multiplexchannels. Note that, where the transmission signal is differentiallycoded and delayed detection is applied, there is no need of sending sucha space-division-multiplex-channel-based pilot signal. Incidentally, howto send a space-division-multiplexed-channel-based pilot signalCP_(k)(t) (frame structure) is the same as the explanation in embodiment1 using FIG. 5.

Now explanation is made on the reception operation at the mobile stationMS.

At first, the n-th SDM-compatible mobile station MSn receives aspace-division-multiplexed radio-frequency signal at mobile-stationantennas 221 in the number of Ns^((n)). The receiver sections 222 in thenumber of Ns^((n)) output the number Ns^((n)) of complex base-bandsignals r_(j) ^((n))(t) comprising I and Q signals due topost-frequency-conversion orthogonal detection, in response to therespective radio-frequency signals in the number of Ns^((n)) received.(Note that j is a natural number equal to or smaller than Ns^((n)).)

Then, space division demultiplex means 721 demultiplexes thespace-division multiplex channels in the number of Nc^((n)) to theSDM-compatible mobile stations MS_(n). The space division demultiplexmeans 721 calculates a channel estimation value h^(n)(j, k) on eachspace division multiplex channel as shown in (Equation 15) by use of aspace-division-multiplex-channel-based pilot signal CPk(t) embeddedindividually in the space-division multiplex channel. Furthermore, thetransmission signal is decoded by use of a decode method correspondingto the space-time coding method used in the space-time coding means 702,thereby outputting a reception data sequence 722. Here, k is a naturalnumber equal to or smaller than the number of space-division multiplexchannels Nc^((n)) for transmission to the SDM-compatible mobile stationsMS_(n). Incidentally, * is a complex conjugate operator and the numberof symbols in the space-division-multiplex-channel-based pilot signalCP_(k)(t) is assumed Nq.

Incidentally, the following is included as another method of spacedivision demultiplex. Namely, when the partial space orthogonalizingmeans 210 is used in SDM transmission to the B-th mobile station MS_(B),singular values are selected Nc in the greater order of those obtainedin singular value resolution of C_(B) as shown in (Equation 13). Byusing a right singular-valued matrix Us=[U₁, U₂, . . . , U_(Nc(B))]constituted by left singular-value vector corresponding to thosesingular values, whose complex-conjugate-interposed matrix (US)^(H) ismultiplied from left on the received signal vector R=[r₁ ^((B))(t), r₂^((B))(t), . . . , r_(Ns(B)) ^((B))(t)]^(T). With this method, a signalcan be demultiplex-received through the respective space-divisionmultiplex channels. In this case, the right singular-valued matrix Us ispreviously notified to the mobile station MS_(B) via the communicationline. Incidentally, as for the number of space division multiplex onesand the kind of the space-division-multiplexed-channel-based pilotsignal, notification is previously made from the base station BS to themobile station MS_(n) by way of the control channel, etc.

The operation to the SDM-uncompatible mobile station MS₁ is similar toembodiment 1.

As described above, the present embodiment is lower in transmission rateto the SDM-compatible mobile stations but can obtain a received qualityimprovement due to an addition of an error correction ability added witha transmission diversity effect in addition to the effect of embodiment1, because of making a space-time coding during spatially multiplextransmission to SDM-compatible mobile stations thereby sending the sameone of data by space division multiplex. This can obtain atransmission-power reduction effect where effecting transmission-powercontrol in a manner to obtain a required received quality. Besides,where transmission power is constant, there can obtain an effect toincrease the communication area where a required received quality is tobe obtained.

In the present embodiment, the coding way and rate at the space-timecoding means can be changed in accordance with propagation environment.This can improve the throughput in compliance with a versatility ofpropagation environments.

Although the present embodiment showed the example of making aspace-time coding during spatially multiplex transmission to theSDM-compatible mobile stations in the downlink, similar application isavailable in the uplink. In this case, space-time coding is applied inthe SDM-compatible mobile station to the space division multiplextransmission signal while decode process is applied in the base stationin compliance with the space-time coding.

INDUSTRIAL APPLICABILITY

As described above, the present invention is useful for a radiocommunication system that mobile stations compatible with spatiallymultiplex transmission and mobile stations uncompatible therewithcoexist within a communication area, and suited in effectively utilizingthe spatial freedom within the base station and improving thecommunication capacity of the radio communication system.

1. A base station apparatus comprising: a deciding section for decidingan allocation for a plurality of mobile stations within a communicationarea, by judging: 1) whether one of the plurality of mobile stations isa space-division-multiplex (SDM) compatible mobile station by use of apredetermined SDM evaluation criterion; and 2) whether another of theplurality of mobile stations is a space-division-multiple-access (SDMA)compatible mobile station to which a SDMA transmission can be appliedalong with the SDM compatible mobile station by use of a predeterminedSDMA evaluation criterion; wherein the SDM evaluation criterion iscalculated based on a channel estimation value and a received channelquality value received from the one of the plurality of mobile stationswithin the communication area; wherein the SDMA evaluation criterion iscalculated based on a received channel quality value received from theanother of the plurality of mobile stations and a spatial correlationcoefficient which is a measure of correlation between a channelestimation value of an already allocated SDMA mobile station of theplurality of mobile stations and a channel estimation value of theanother of the plurality of mobile stations; wherein the another of theplurality of mobile stations is judged to be a SDMA compatible mobilestation when the spatial correlation coefficient is below apredetermined spatial correlation coefficient; a partial-spaceorthogonalizing section for performing a weighting process, forenhancing orthogonality over a propagation path for a SDM transmission,on a first transmission data sequence to be sent by the SDM transmissionto the SDM compatible mobile station; a beam forming section for forminga plurality of transmission beams for an output of the partial-spaceorthogonalizing section in order to send the first transmission datasequence by the SDM transmission to the SDM compatible mobile stationand a single transmission beam for a second transmission data sequenceto be sent by SDMA transmission to the SDMA compatible mobile station;and a plurality of antennas for simultaneously transmitting the firsttransmission data sequence using the plurality of transmission beams andthe second transmission data sequence using the single transmissionbeam, wherein, in a case that the SDM compatible mobile station and aSDM uncompatible mobile station are allocated for SDMA communication ata same time, the beam forming section forms a single maximum ratiosynthetic directional transmission beam in a single space divisionmultiplex channel to the SDM uncompatible mobile station, and forms aplurality of other directional transmission beams in a plurality ofother space division multiplex channels to the SDM compatible mobilestation, wherein the directional transmission beams are simultaneouslytransmitted to the SDM uncompatible and SDM compatible mobile stationsat the same frequency.
 2. The base station apparatus according to claim1, wherein forming the transmission beam for reducing the interferenceby the beam forming section is to form the transmission beam from thetransmission data sequence to the allocated SDMA compatible mobilestation and an output of the partial-space orthogonalizing section, in amanner being orthogonal to a channel estimation matrix on another mobilestation to access simultaneously.
 3. A base station apparatus accordingto claim 2, wherein, in a case that the SDMA mobile stations include aSDM compatible mobile station and a SDM uncompatible mobile station,another transmission beam to the SDM uncompatible mobile station isformed by use of a complex-conjugate-transposition of a channelestimation matrix on the SDM uncompatible mobile station, and thetransmission beam to the SDM compatible mobile station is formed in amanner being orthogonal to a channel estimation matrix on another SDMAmobile stations to access simultaneously.
 4. The base station apparatusaccording to claim 1, wherein, forming the transmission beam forreducing the interference by the beam forming section is to form thetransmission beam orthogonal to a channel estimation matrix on anotherof a SDM uncompatible mobile station and the SDM compatible mobilestation to access simultaneously.
 5. The base station apparatusaccording to claim 1, further comprising space-time coding means formaking a space-time coding process on the transmission data sequence tothe SDM compatible mobile station, the transmission data sequencespace-time-coded being outputted to the partial-space orthogonalizingsection.
 6. A base station apparatus according to claim 1, wherein, in acase that the SDMA mobile stations include a SDM compatible mobilestation and a SDM uncompatible mobile station, another transmission beamto the SDM uncompatible mobile station is formed by use of acomplex-conjugate-transposition of a channel estimation matrix on theSDM uncompatible mobile station, and the transmission beam to the SDMcompatible mobile station is formed in a manner being orthogonal to achannel estimation matrix on another SDMA mobile stations to accesssimultaneously.